RCMD(3SOCKET)RCMD(3SOCKET)NAME
rcmd, rcmd_af, rresvport, rresvport_af, ruserok - routines for return‐
ing a stream to a remote command
SYNOPSIS
cc [ flag ... ] file... -lsocket-lnsl [ library... ]
#include <netdb.h>
#include <unistd.h>
int rcmd(char **ahost, unsigned short inport, const char *luser,
const char *ruser, const char *cmd, int *fd2p);
int rcmd_af(char **ahost, unsigned short inport, const char *luser,
const char *ruser, const char *cmd, int *fd2p, int af);
int rresvport(int *port);
int rresvport_af(int *port, int af);
int ruserok(const char *rhost, int suser, const char *ruser,
const char *luser);
DESCRIPTION
The rcmd() function is used by the superuser to execute a command on a
remote machine with an authentication scheme based on reserved port
numbers. An AF_INET socket is returned with rcmd(). The rcmd_af() func‐
tion supports AF_INET, AF_INET6 or AF_UNSPEC for the address family. An
application can choose which type of socket is returned by passing
AF_INET or AF_INET6 as the address family. The use of AF_UNSPEC means
that the caller will accept any address family. Choosing AF_UNSPEC pro‐
vides a socket that best suits the connectivity to the remote host.
The rresvport() function returns a descriptor to a socket with an
address in the privileged port space. The rresvport_af() function is
the equivalent to rresvport(), except that you can choose AF_INET or
AF_INET6 as the socket address family to be returned by rresvport_af().
AF_UNSPEC does not apply to the rresvport() function.
The ruserok() function is a routine used by servers to authenticate
clients that request as service with rcmd.
All of these functions are present in the same file and are used by the
in.rshd(1M) server among others.
The rcmd() and rcmd_af() functions look up the host *ahost using getad‐
drinfo(3SOCKET) and return −1 if the host does not exist. Otherwise,
*ahost is set to the standard name of the host and a connection is
established to a server residing at the Internet port inport.
If the connection succeeds, a socket in the Internet domain of type
SOCK_STREAM is returned to the caller. The socket is given to the
remote command as standard input (file descriptor 0) and standard out‐
put (file descriptor 1). If fd2p is non-zero, an auxiliary channel to a
control process is set up and a descriptor for it is placed in *fd2p.
The control process returns diagnostic output file (descriptor 2) from
the command on the auxiliary channel. The control process also accepts
bytes on this channel as signal numbers to be forwarded to the process
group of the command. If fd2p is 0, the standard error (file descriptor
2) of the remote command is made the same as its standard output. No
provision is made for sending arbitrary signals to the remote process,
other than possibly sending out-of-band data.
The protocol is described in detail in in.rshd(1M).
The rresvport() and rresvport_af() functions are used to obtain a
socket bound to a privileged port number. The socket is suitable for
use by rcmd() and rresvport_af() and several other routines. Privileged
Internet ports are those in the range 1 to 1023. Only the superuser is
allowed to bind a socket to a privileged port number. The application
must pass in port, which must be in the range 512 to 1023. The system
first tries to bind to that port number. If it fails, the system then
tries to bind to another unused privileged port, if one is available.
The ruserok() function takes a remote host name returned by the geth‐
ostbyaddr() function with two user names and a flag to indicate whether
the local user's name is that of the superuser. See gethostby‐
name(3NSL). The ruserok() function then checks the files
/etc/hosts.equiv and possibly .rhosts in the local user's home direc‐
tory to see if the request for service is allowed. A 0 value is
returned if the machine name is listed in the /etc/hosts.equiv file, or
if the host and remote user name are found in the .rhosts file. Other‐
wise, the ruserok() function returns −1. If the superuser flag is 1,
the /etc/hosts.equiv is not checked.
The error code EAGAIN is overloaded to mean "All network ports in use."
RETURN VALUES
The rcmd() and rcmd_af() functions return a valid socket descriptor
upon success. The functions returns −1 upon error and print a diagnos‐
tic message to standard error.
The rresvport() and rresvport_af() functions return a valid, bound
socket descriptor upon success. The functions return −1 upon error with
the global value errno set according to the reason for failure.
FILES
/etc/hosts.equiv
system trusted hosts and users
~/.rhosts
user's trusted hosts and users
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌───────────────┬─────────────────┐
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├───────────────┼─────────────────┤
│MT-Level │ Unsafe │
└───────────────┴─────────────────┘
This interface is Unsafe in multithreaded applications. Unsafe inter‐
faces should be called only from the main thread.
SEE ALSOrlogin(1), rsh(1), in.rexecd(1M), in.rshd(1M), Intro(2), getad‐
drinfo(3SOCKET), gethostbyname(3NSL), rexec(3SOCKET), attributes(5)
Feb 10, 2004 RCMD(3SOCKET)
